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First archeointensity results from Portuguese potteries (1550-1750 AD)

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Abstract

Geomagnetic field variations at archeomagnetic timescales can be obtained from well-dated heated structures and archeological potsherds. Here, we present the first archeointensity results obtained on Portuguese ceramics (1550 to 1750 AD) collected at Brazilian archeological sites. The results are compared to those obtained from Western Europe and currently available geomagnetic field models. Continuous thermomagnetic and IRM acquisitions curves indicate that Ti-poor titanomagnetite is responsible for the remanence in these ceramic fragments. Five fragments (24 samples) out of twelve analyzed yielded reliable intensity estimates. The row archeointensity data were corrected for TRM anisotropy and cooling rate effect. The mean dipole moments are obtained for three different age intervals: 1550±30 AD, 1600±30 AD and 1750±50 AD. Mean intensities vary from 37.9±4.2 μT to 54.8±7.6 μT in agreement with the previously reported data for 1550 AD and 1750 AD. Relatively weaker, but still highly dispersed, values were obtained for 1600 AD ceramics.

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Correspondence to Gelvam A. Hartmann.

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Key words

  • Archeointensity
  • secular variation
  • cooling rate correction
  • Portuguese pottery